code: def atts_ssim_diff():
      return {"a": np.zeros((16, 16)), "b": np.ones((16, 16))}
  
imports: import pytest
  from pytest_lazyfixture import lazy_fixture
  from quantus.functions.loss_func import mse
  from quantus.functions.similarity_func import *
label_desc: Use image node_id 8 for calling a global function with example usage: atts_ssim_diff() and returns: dict